(1) Field of the Invention
The present invention relates to a large structure for use in outer space, i.e., an deployable (expandable) truss structure which can be used in a large antenna, a space station or the like. In addition, the deployable truss structure can be utilized as a portable temporary emergency structure on the earth, the moon, Mars or the like.
(2) Description of the Related Art
A structure for outer space can be carried as a payload in to space by a rocket to be launched such as an H-II rocket. The volume and weight of the payload are limited by the carrying power of the rocket to be launched, and therefore the structure must be designed so as to be as lightweight and as compact as possible. In the case of a truss structure which is a typical example of a large space structure, the limitation of the volume is more important than that of the weight. On the basis of the above background, much attention has been paid to an deployable truss structure, as a promising space structure, whose volume can be decreased by folding it at the time of the launch and which can be deployed in space after the launch to take a final formation.
In general, the deployable truss structure is constituted so as to form one large deployable truss structure in which deployable members called cells, each comprising a plurality of side structures foldable in one plane, are periodically joined to each other, while the adjacent side structures hold on to each other in common. In order to enlarge the deployable truss structure, the following two means can be considered. One of the means is to enlarge the size of the above cells when they are deployed, and the other is to increase the number of cells.
A typical example of the deployable truss structure is a hexalink truss 1. FIG. 11 shows an overall constitutional view of the hexalink truss 1, and FIG. 12 shows a hexagonal pillar cell 2 constituting the hexalink truss 1. As shown in FIG. 12, the cell 2 is constituted by joining the same side structures 3 in a circular form. FIG. 13 shows a constitutional view of the side structure. As shown in FIG. 13, an upper foldable member 5 is bound to upper portions of two vertical members 4 so as to be bridged between them. The upper foldable member 5 is foldable at its center position, and it is bound to the vertical member 4 and an upper foldable member end portion 6 via a hinge. The upper foldable member 5 is rotatable relative to the vertical member 4 in a plane including a synchronous mechanism 7. Furthermore, the upper foldable member end portion 6 is provided with a helical spring 8, which is an deployable drive source of the side structure 3. In addition, a slide hinge 9 is bound to the lower portion of each of the two vertical members 4, and this hinge is movable along the vertical member 4. The slide hinge 9 is bound, via the synchronous mechanism 7, to the upper portion of the vertical member 4 which is different from the vertical member 4 which can move by itself. The synchronous mechanism 7 comprises two slant members which are bound to each other via a hinge so as to be relatively rotatable at a center portion 10. Moreover, a lower end portion 11 of this synchronous mechanism 7 is bound to the vertical member 4 via the slide hinge 9, and in the plane including the synchronous mechanism 7, the vertical member 4 and the synchronous mechanism 7 are bound to each other so as to be relatively rotatable. Furthermore, a lower foldable member 12 is foldable at its center position as in the case of the upper foldable material 5, and the lower foldable material 5 is bound to the vertical member 4 via the slide hinge 9 so as to be rotatable relative to the vertical member 4 in the plane including a synchronous mechanism 7.
The side structure 3 having the above-mentioned member constitution can be deployed, taking formations shown in FIG. 14A to FIG. 14C. That is to say, by torque generated by the helical spring 8, the upper foldable member 5 is opened, and simultaneously, force in a parallel direction acts on the two vertical members 4, so that they move in the parallel direction. With this movement, the synchronous mechanism 7 bound to the vertical members 4 is opened, and simultaneously, the slide hinges 9 bound to the synchronous mechanism 7 slide forward along the vertical members 4 and the lower foldable members 12 are also opened with the movement in the parallel direction of the vertical members 4. Through the above steps, the side structure 3 can accomplish the deploying operation in one plane.
Each cell is constituted by joining a plurality of the side structures in a circular form, but since the adjacent side structures constituting the cell mutually hold some of the movable parts in common, all of the side structures in the cell can synchronously carry out the deploying operation. In the case of the above hexalink truss 1, the adjacent side structures 3 in the cell hold the vertical members 4 and the slide hinges 9 in common, whereby all of the side structures 3 in the cell can synchronously carry out the deploying operation. FIG. 15 shows a formation state in the middle of the deployment of the cell. Therefore, the hexalink truss 1 is the deployable truss structure in which a plurality of the cells 2 are bound to each other, holding all of the adjacent side structures 3 in common, and therefore, in the deployment process of the hexalink truss 1, all of the side structures 3 constituting the hexalink truss 1 can synchronously be deployed.
The feature of such an deployable truss structure resides in that the side structures of all the adjacent cells are held in common among the adjacent side structures themselves. Accordingly, such an deployable truss structure has characteristics that under mechanically ideal conditions no looseness of the hinges is present, and all of the deployable mechanisms constituting the structure can be synchronously deployed during the deploying operation. Therefore, in the case that the number of the cells regarding one deploying operation, i.e., the number of the movable constitutional parts is increased for the purpose of the enlargement of an antenna, it is necessary to significantly increase the movable reliability of each of the mechanical parts. In other words, the deployment performance depends on certain design factors and there is a problem that the enlargement of the deployable truss structure is difficult owing to the increase in the number of deployable constitutional parts.